Instrument for combustible gas detection

Abstract

A method for detecting combustible gases or vapours using a combustible gas sensor or pellistors includes the steps of keeping the combustible gas sensor or the pellistor beads inactive until an oxygen sensor indicates a variation from a reference level of oxygen, such variation representing the potential presence of combustible gases or vapours.

I claim:  
     
       1. A method for the detection of combustible gases or vapours in an atmosphere using a sensor, includes the steps of exposing the sensor to the atmosphere, sensing the atmosphere for the level of oxygen, activating the sensor responsive to a predetermined level of oxygen change indicating the presence of a contaminant gas or vapour, detecting the level of combustible gases or vapours in the atmosphere using the sensor, and maintaining the activation of the sensor or deactivating the sensor dependent upon the level of contaminant gases of vapours detected. 
     
     
       2. A method for the detection of combustible gases or vapours in an atmosphere using pellistors comprising, including the steps of exposing the pellistors to the atmosphere, sensing the atmosphere for the level of oxygen using an oxygen sensor, activating the pellistors responsive to a predetermined level of oxygen change indicating the presence of a contaminant gas or vapour, detecting the level of combustible gases or vapours in the atmosphere using the pellistors, and maintaining activation of the pellistors or deactivating the pellistors dependent upon the level of contaminant gases or vapours detected. 
     
     
       3. A method according to  claim 2  in which the combustible gas sensor, the pellistors and the oxygen sensor are pre-calibrated. 
     
     
       4. A method according to  claim 1  in which the oxygen sensor is calibrated to a predetermined level a variation from which is adapted to activate the combustible gas sensor or pellistors. 
     
     
       5. A method according to  claim 1  in which the combustible gas sensor is or the pellistors are calibrated to remain activated upon the contamination by a combustible gas or vapour attaining or exceeding a predetermined level. 
     
     
       6. A method according to  claim 1  in which the activation of the combustible gas sensor or the pellistors is continuous or cyclic on an on/off basis. 
     
     
       7. A method according to  claim 4  which the sensor is adapted to provide an alarm when the predetermined level of combustible gas or vapour is exceeded. 
     
     
       8. A method according to  claim 5  in which the pellistors are adapted to provide an alarm when the predetermined level of combustible gas or vapour is exceeded. 
     
     
       9. An instrument for the detection of combustible gases or vapours in an atmosphere, includes a sensor for detecting the combustible gas or vapour, an oxygen sensor adapted to sense a change in the level of oxygen in the atmosphere, and control means for controlling the activation of the combustible gas sensor responsive to the sensed level of oxygen in the atmosphere falling below a predetermined reference level of oxygen. 
     
     
       10. An instrument for the detection of combustible gases or vapours in an atmosphere including pellistors comprising a detector bead and a compensator bead, an oxygen sensor adapted to sense a change in the level of oxygen in the atmosphere, and control means for controlling activation of the pellistors responsive to the sensed level of oxygen in the atmosphere falling below a predetermined reference oxygen level. 
     
     
       11. An instrument according to  claim 8  in which there is provided a power source. 
     
     
       12. An instrument according to  claim 8  in which the oxygen sensor is an electrochemical oxygen sensor. 
     
     
       13. An instrument according to  claim 11  in which when the instrument is in use the oxygen sensor is maintained constantly in an active mode. 
     
     
       14. An instrument according to  claim 8  in which the control means is a microprocessor.